The present invention relates to cardiac pacemakers.
Cardiac stimulation is presently a clinically and therapeutically accepted method for correcting various degrees of heart block and specific other arrhythmias. One recently developed technique, sometimes termed "physiological stimulation", involves stimulation of not just the ventricles or just the atria, but both sets of chambers. Studies have been conducted of the so-called sequential stimulation over a wide range of stimulation parameters in connection with a study of the hemodynamic properties of the heart, as reported in an article by Samet et al, entitled "Hemodynamic Sequelae of Atrial, Ventricular and Sequential Atrial Ventricular Pacing in Cardiac Patients", American Heart Journal, Volume 72, pages 725-729, December, 1966.
Earlier than that, p-wave synchronous coupling of the stimulation of both chambers was found to produce substantially better antiarrhythmia properties than stimulation of the ventricle exclusively. As described by Nathan et al in an article entitled "An Implantable Synchronous Pacemaker for the Long Term Correction of Complete Heart Block", American Journal of Cardiology, Volume 11, page 362, 1963. Bradycardia have been treated with a corresponding ventricular rhythm which completed with, or was out of synchronism with, the true sinus rate.
Implantable versions of AV-sequential pacemakers, as they are disclosed in U.S. Pat. No. 3,747,604 and which are based on the work reported in the above-cited article by Samet et al, provided atrial escape stimuli before ventricular escape stimuli so that the protection against arrhythmias is augmented particularly in the bradycardial area. In this connection, the term "escape stimuli" is intended to mean that the artificial cardiac pacemaker emits a stimulation pulse unless a corresponding signal appears from the heart itself within a given interval.
Studies and observations with arrhythmias described by Castellanos et al in the article entitled "Preliminary Studies with an Implantable Multimode A-V Pacemaker for Reciprocating Atrioventricular Tachycardias". PACE, Volume 3, No. 3, May, 1980, indicate ways in which arrhythmias can be initiated, eliminated and suppressed by suitable stimulation of one of the two chambers of the heart, even if in some patients coupling is effected in the reverse direction.
The literature on cardiac arrhythmias is replete with diagrams and listings of criteria for the "reentry-arrhythmias" of the dominant type where two stimulation pathways must exist to maintain the arrhythmia. It is also shown there that the delay period of the loop must be relatively long to meet the requirement for sustained reentry. All prior art attempts to terminate tachyarrhythmias by stimulation have the drawback that the success quota in the various methods per se is not yet satisfactory.